How to create a realistic tooth enamel material?
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Good results can be done with tooth geometries that consist of 2 surfaces: dentin (refraction 1,45) and enamel (refraction 1.7).

The tooth is an anisotropic volume with numerous layers non of which is actualy solid.

Front-lit:



Back-lit:



Can you give us some dental scan or something? That way I can do some tests in the evening.

It should be mix of sss and transparent for the enamel with glossy on surface and yellow tinted volume absorption for dentin.

This should yield what you want. Adding the refraction and anisotropic element should also help but maybe that will be just an overkill..